The RICG plugin does not let you specify any image size or crop by itself. It takes the predefined image sizes (small, medium, full) and custom image sizes to do his work. It’s sole purpose is to deliver the image of a given size that fits within the area defined in HTML, taking retina/hi-dpi screens into account.
Because you can create your own image sizes with the
add_image_size function in your functions.php, you can also specify how to crop these images. You should check the WordPress Codex to see what possibilities this function offers: https://developer.wordpress.org/reference/functions/add_image_size/
If you need more advanced sizing and/or cropping you should check other alternatives.
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